Render Targets

[recp]

• Multiple render targets
• Off screen [multiple] framebuffers
• Render target manager
• Framebuffer manager

[recp]

By starting now, texture units are managed by library and they are being hidden from public api.
Maybe to supporting this idea and make it more robust we could create GkTexture or something like GkTextureProxy for render targets to continue hide texture unit management from public.